The present invention relates to a pattern formation method, and more particularly, it relates to a method of forming a pattern out of an etching target film formed on a semiconductor substrate by conducting dry etching on the etching target film by using, as a mask, a patterned photosensitive film formed on the etching target film with an anti-reflection coating of an organic material disposed therebetween.
In accordance with downsizing of a system using complicated semiconductor integrated circuits, it has become very difficult to transfer a complicated circuit onto a small chip by pattern lithography using a patterned photosensitive film as a mask. This is for the following reason: As the wavelength of an energy beam irradiating an etching target film is shortened, the reflectance of the energy beam is increased. Therefore, the energy beam is affected by an irregular step shape of the photosensitive film so as to be reflected in irregular directions after passing through the photosensitive film. As a result, an unnecessary portion (i.e., a portion that should not be irradiated with the energy beam) is exposed in the photosensitive film. This leads to a large number of artificial defects and dimensional variation in a pattern formed by the lithography.
As a countermeasure, it is proposed that an anti-reflection coating for absorbing the energy beam is formed below the photosensitive film so as to prevent the energy beam from being reflected in the irregular directions after passing through the photosensitive film.
Now, a conventional pattern formation method using an anti-reflection coating will be described with reference to FIGS. 4(a) and 4(b).
As is shown in FIG. 4(a), an anti-reflection coating 3 of an organic material for absorbing an energy beam is deposited on an etching target film 2 formed on a semiconductor substrate 1, and a photosensitive film is then deposited on the anti-reflection coating 3. Next, the photosensitive film is irradiated with an energy beam through a mask, and an exposed or unexposed portion of the photosensitive film is removed by using a developer, thereby forming a patterned photosensitive film 4 out of the exposed or unexposed portion. Subsequently, the anti-reflection coating 3 is dry etched by using the patterned photosensitive film 4 as a mask, thereby removing an area of the anti-reflection coating 3 corresponding to an opening of the patterned photosensitive film 4.
Next, as is shown in FIG. 4(b), the etching target film 2 is dry etched by using the patterned photosensitive film 4 as a mask, and the anti-reflection coating 3 and the photosensitive film 4 are then removed. In this manner, a pattern 2A of the etching target film 2 is formed on the semiconductor substrate 1.
When the pattern 2A is formed in the aforementioned manner, the energy beam having passed through the photosensitive film 4 is absorbed by the anti-reflection coating 3 disposed between the etching target film 2 and the patterned photosensitive film 4. Accordingly, even when the photosensitive film 4 has an irregular step shape, the photosensitive film 4 can be prevented from being exposed to irregularly reflected light. As a result, the pattern 2A of the etching target film 2 can be dimensionally accurately formed.
However, a reaction product 5 is generated on an interface between the anti-reflection coating 3 and the photosensitive film 4 as is shown in FIG. 4(a), so that the reaction product 5 remains on the etching target film 2 after removing the anti-reflection coating 3 and photosensitive film 4.
Thereafter, in the dry etching of the etching target film 2 by using the patterned photosensitive film 4 as a mask, the reaction product 5 remaining on the etching target film 2 serves as a mask. Accordingly, as is shown in FIG. 4(b), a residue 6 of the etching target film 2 can be disadvantageously formed in an area to be etched (i.e., a space area) in the etching target film 2 or a pattern wall 2a of the etching target film 2 required to be vertical can be formed in an irregular shape. In particular, the residue 6 derived from the reaction product 5 has a very small size of 0.1 xcexcm or less, and is a specific residue basically different from a residue formed due to insufficient conditions for the dry etching of the etching target film 2 (for example, a residue having a size of 0.2 xcexcm or more).
Also, the residue 6 is generated uniformly without being affected by the aperture ratio of the pattern of the photosensitive film 4, namely, regardless of the density of the pattern. Accordingly, the residue 6 is formed also in a space between patterns formed at a high density.
Therefore, a method of removing the reaction product 6 generated on the interface between the anti-reflection coating 3 and the photosensitive film 4 together with the anti-reflection coating through the dry etching of the anti-reflection coating 3 is considered, but this method is not effective as a method of forming a pattern of the etching target film for the following reason: In the dry etching of the anti-reflection coating 3 by using the patterned photosensitive film 4 as a mask, a larger part of the anti-reflection coating 3 is preferably removed while a smaller part of the patterned photosensitive film 4 is preferably removed. However, both the anti-reflection coating 3 and the photosensitive film 4 are made from organic materials, and hence, they have very similar dry etching characteristics (such as an etching rate). Accordingly, when the anti-reflection coating 3 is dry etched under conditions where the patterned photosensitive film 4 can be less removed through the dry etching, large parts of the reaction product 5 and the anti-reflection coating 3 remain on the etching target film 2. In contrast, when the anti-reflection coating 3 is dry etched under conditions where the reaction product 5 cannot remain, the patterned photosensitive film 4 is also removed through the dry etching and cannot work as a mask. In addition, even when the dry etching is actually conducted so as to remove the reaction product 5 without considering the masking function of the photosensitive film 4 (for example, by elongating the etching time or the like), the residue 6 cannot be reduced.
Furthermore, when a dry etching process in which a deposition is formed on the wall of the anti-reflection coating 3 is adopted so as to improve the dimensional controllability on the anti-reflection coating 3, the deposition peeled off from the wall of the anti-reflection coating 3 can be easily adhered onto the etching target film 2. Therefore, the deposition works as a mask, resulting in forming the residue 6 of the etching target film 2.
When the residue 6 of the etching target film 2 remains on the semiconductor substrate 1 or when the pattern wall 2a of the etching target film 2 is formed in an irregular shape, the following problems are caused:
In the case where the etching target film 2 is made from a conductive material such as polysilicon, wire patterns formed in the same conductive layer in a resultant semiconductor integrated circuit device can be electrically connected with each other through the conductive residue 6. Alternatively, a conductive layer formed on the semiconductor substrate 1 can be electrically connected through the conductive residue 6 with a wire pattern formed on the conductive layer with an interlayer insulating film sandwiched therebetween. Accordingly, a leakage current flows between the wire patterns or between the conductive layer and the wire pattern. As a result, the semiconductor integrated circuit device can be disadvantageously degraded in its characteristic or yield.
FIG. 5 is an enlarged view of an area surrounded with a dashed line in FIG. 4(b). As is shown in FIG. 5, a gate electrode 7 of a polysilicon film corresponding to the etching target film 2 is formed on the semiconductor substrate 1, and the residue 6 of the polysilicon film remains in a region between the gate electrodes 7 in the semiconductor substrate 1, namely, in a source/drain region. Also, a sidewall 8 of an insulating material such as Si3N4, TEOS and HTO is formed on the side face of the gate electrode 7, and the surfaces of the gate electrode 7 and the source/drain region are silicided with TiSi2 or the like to be covered with a silicide layer 9. However, since the shape of the side face of the gate electrode 7 is irregular, the gate electrode 7 is bared on the sidewall 8, and the silicide layer 9 is formed not only on the bared portion of the gate electrode 7 on the sidewall 8 but also on the surface of the residue 6 of polysilicon.
Accordingly, the gate electrode 7 and the source/drain region are electrically connected with each other through the silicide layer 9 on the gate electrode 7 or on the residue 6. Thus, an abnormal leakage current unavoidably flows between the gate electrode 7 and the source/drain region, resulting in degrading the device characteristic.
In view of the aforementioned conventional problems, the object of the invention is, while using an anti-reflection coating of an organic material disposed between an etching target film and a photosensitive film, preventing generation of a reaction product on the anti-reflection coating, so as to reduce the number of residues of the etching target film.
As a result of examination on the cause of generating the reaction product on the interface between the anti-reflection coating and the photosensitive film, the present inventors have found that the reaction product is generated in accordance with a mechanism described below and that a sulfonyl compound has a function to suppress the generation of the reaction product.
On the interface between the photosensitive film and the anti-reflection coating of an organic material, an aromatic radical is generated from a photosensitive material included in the photosensitive film through the exposure to an energy beam. Then, the radical causes a chain reaction with an aromatic compound included in the anti-reflection coating, resulting in generating a high molecular aromatic compound (that is, the reaction product 5) having high etching resistance. As a result, residues remain in a space portion of a pattern formed after the dry etching of the etching target film.
In particular, when the photosensitive film contains an acid generator including, for example, onium salt, a larger amount of the aromatic reaction product is generated on the interface between the anti-reflection coating and the photosensitive film through the irradiation with the energy beam (namely, the aromatic reaction product is generated also in the photosensitive film). Therefore, the number of residues is increased.
However, when a sulfonyl compound is added, an aryl radical is generated as a side product through the exposure to the energy beam. In this case, when the aromatic radical generates the high molecular aromatic compound (the reaction product 5) through the radical chain reaction, the aryl radical causes a coupling reaction, resulting in preventing the chain reaction of the aromatic radical. In other words, the aryl radical works as a reaction inhibitor against the chain reaction of the aromatic radical. Accordingly, the generation of the high molecular aromatic compound (the reaction product 5) having high etching resistance can be prevented by adding the sulfonyl compound. Thus, the pattern formed after the dry etching of the etching target film can be free from the residues.
On the basis of the aforementioned findings, according to the present invention, the sulfonyl compound is included in the photosensitive film, so that the aromatic reaction product can be prevented from being generated on the interface between the anti-reflection coating and the photosensitive film.
Specifically, the pattern formation method of this invention comprises a first step of depositing an anti-reflection coating of an organic material for absorbing an energy beam on an etching target film formed on a semiconductor substrate; a second step of depositing a photosensitive film on the anti-reflection coating; a third step of forming a patterned photosensitive film by irradiating the photosensitive film with an energy beam and selectively removing an exposed or unexposed portion of the photosensitive film; and a fourth step of forming a pattern out of the etching target film by conducting dry etching on the etching target film by using the patterned photosensitive film as a mask, wherein the photosensitive film is made from a photosensitive material including a sulfonyl compound.
In the pattern formation method of this invention, since the photosensitive film includes the sulfonyl compound, an acid including aryl is generated from the sulfonyl compound through the irradiation of the photosensitive film with the energy beam, so that the generated acid including aryl can prevent the radical reaction on the interface between the anti-reflection coating and the photosensitive film. Accordingly, the aromatic reaction product can be prevented from being generated on the interface between the anti-reflection coating and the photosensitive film. Therefore, when the pattern is formed out of the etching target film by conducting the dry etching on the etching target film by using the patterned photosensitive film and anti-reflection coating as masks, the number of residues of the etching target film formed on the semiconductor substrate can be decreased.
In the case where the etching target film is made from a conductive film, wire patterns formed in the same conductive layer can be electrically connected with each other or a conductive layer formed on a semiconductor substrate can be electrically connected with a wire pattern through the conductive residue in a semiconductor integrated circuit device. In such a case, a leakage current can flow between the wire patterns or between the conductive layer and the wire pattern, resulting in degrading the characteristic of the semiconductor integrated circuit device. However, when the pattern formation method of this invention is adopted, such characteristic degradation can be definitely avoided.
In the pattern formation method of this invention, the sulfonyl compound is preferably used as an acid generator.
In this manner, even when the photosensitive film does not include an acid generator for generating an acid, the sulfonyl compound included in the photosensitive film can generate an acid. Therefore, the reaction product generated by the acid generator, and furthermore, the number of residues can be reduced.
In the pattern formation method of this invention, the photosensitive film can include an alkali refractory resin and an acid generator for generating an acid, such as onium salt.
In this manner, since the photosensitive film includes the sulfonyl compound and the sulfonyl compound prevent the generation of the reaction product from the acid generator such as onium salt, the increase in the number of residues derived from the reaction product can be suppressed.
In the pattern formation method of this invention, the photosensitive film preferably includes an alkali refractory resin and does not include an acid generator for generating an acid.
In the pattern formation method of this invention, the fourth step preferably includes a step of patterning the anti-reflection coating through dry etching of the anti-reflection coating by using the patterned photosensitive film as a mask and by using a sulfur etching gas, and conducting the dry etching of the etching target film by using the patterned photosensitive film and anti-reflection film as masks, whereby forming the pattern out of the etching target film.
In this manner, the selectivity to the etching target film can be improved, and the dimensional variation of the pattern of the etching target film can be reduced. In addition, the number of residues formed out of the etching target film on the semiconductor substrate can be decreased.